A transformer is used to provide galvanic isolation and to connect systems at different voltage levels. It is one of the largest and most expensive component in power systems. The central idea behind a power electronic transformer (PET), also known as solid state transformer (SST), is to reduce the size of the transformer by increasing the frequency of operation with power electronic converters. Steady reduction in the cost of the semiconductor switches and the advent of advanced magnetic materials with very low loss density and high saturation flux density implies economic viability and feasibility of a design with high power density. Due to additional features like on-demand reactive power support, voltage and frequency regulation etc., PET has been identified as an enabling technology for the modernization of the electric power distribution system. PET can also be employed for high power density adjustable speed electrical machine drives, for example in wind power generation and traction drives. State of the art multi-stage PETs are less efficient and have a larger foot-print compared to single-stage PETs (all silicon solution). In this talk we will explore a novel single-stage PET which is particularly suitable for compact isolated pulse width modulated (PWM) AC drives. The proposed PET with a high frequency transformer (HFT), generates adjustable frequency and magnitude PWM three-phase AC voltage waveform from a balanced three-phase AC voltage source. This topology along with the proposed control has the following advantages : 1) bi-directional power ow; 2) open-loop input power factor correction; 3) common-mode voltage suppression at the load end; 4) high quality output voltage waveform (comparable to conventional space vector PWM); and 5) minimization of output voltage loss, common-mode voltage switching and distortion of the load current waveform due to the commutation of leakage energy. A source based commutation of currents, associated with the energy stored in the leakage inductance of the HFT (termed as leakage energy), has been proposed. This results in soft-switching of the load side converter and recovery of the leakage energy. It also obviates the need for additional snubber circuits.
Kaushik Basu received the BE degree in electrical engineering from the Bengal Engineering and Science University, Shibpore, India, in 2003, the MS degree in electrical engineering from the Indian Institute of Science, Bangalore, India, in 2005, and the PhD degree in electrical engineering with a minor in mathematics from the University of Minnesota, Minneapolis, in 2012, respectively. He was a Design Engineer with ColdWatt India in 2006. He is currently the Electronics and Control Engineer with Dynapower Company LLC, USA. His research interests include High frequency link converters, PWM techniques and Grid tied converters with storage and renewable energy sources.